Fluorinated hydrocarbons have many uses, one of which is as a refrigerant. Such refrigerants include dichlorodifluoromethane (CFC-12) and chlorodifluoromethane (HCFC-22).
In recent years it has been pointed out that certain kinds of fluorinated hydrocarbon refrigerants released into the atmosphere may adversely affect the stratospheric ozone layer. Although this proposition has not yet been completely established, there is a movement toward the control of the use and the production of certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) under an international agreement.
Accordingly, there is a demand for the development of refrigerants that have a lower ozone depletion potential than existing refrigerants while still achieving an acceptable performance in refrigeration applications. Hydrofluorocarbons (HFCs) have been suggested as replacements for CFCs and HCFCs since HFCs have no chlorine and therefore have zero ozone depletion potential.
In refrigeration applications, a refrigerant is often lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. In addition, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration equipment, which may cause the refrigerant to become flammable or to have poor refrigeration performance.
Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition that includes at least one fluorinated hydrocarbon.
Refrigerant compositions of the invention which are non-azeotropic, i.e., zeotropic may also be useful in vapor compression systems. See Didion, The Role of Refrigerant Mixtures as Alternatives, Proceedings of ASHRAE CFC Technology Conference, Gaithersburg, Md., 1989. Non-azeotropic mixtures can boil over a wide temperature range under constant pressure conditions and create a temperature glide in the evaporator and in the condenser. This temperature glide can reduce the energy required to operate the system by taking advantage of the Lorenz cycle. The preferred method involves the use of counter current flow evaporator and/or condenser heat exchangers in which the refrigerant and the heat transfer fluid flow countercurrently. This method decreases the temperature difference between the evaporating and condensing refrigerant but maintains a high enough temperature difference between the refrigerant and external heat transfer fluid to effectively transfer heat. Another benefit of this type of system is that pressure differences are also minimized. This can result in an improvement in energy efficiency and/or capacity versus conventional systems.
Azeotropic, azeotrope-like, or zeotropic compositions that include a fluorinated hydrocarbon are also useful as blowing agents in the manufacture of closed-cell polyurethane, phenolic and thermoplastic foams, as propellants in aerosols, as heat transfer media, electronic gases, plasma etchants, gaseous dielectrics, fire extinguishing agents, power cycle working fluids such as for heat pumps, inert media for polymerization reactions, fluids for removing particulates from metal surfaces, as carrier fluids that may be used, for example, to place a fine film of lubricant on metal parts, as buffing abrasive agents to remove buffing abrasive compounds from polished surfaces such as metal, as displacement drying agents for removing water, such as from jewelry or metal parts, as resist developers in conventional circuit manufacturing techniques including chlorine-type developing agents, or as strippers for photoresists when used with, for example, a chlorohydrocarbon such as 1,1,1-trichloroethane or trichloroethylene.
A farther utility for the nitrous oxide compositions of the present invention is a process for etching a thin film device comprising the steps of:
a) contacting said device with at least one nitrous oxide composition; and PA1 b) forming a plasma from said composition during said contacting whereby said device is etched. PA1 The composition can be defined as an azeotrope of A, B, C (and D . . . ) since the very term "azeotrope" is at once both definitive and limitative, and requires that effective amounts of A, B, C (and D . . . ) for this unique composition of matter which is a constant boiling composition. PA1 It is well known by those skilled in the art, that, at different pressures, the composition of a given azeotrope will vary at least to some degree, and changes in pressure will also change, at least to some degree, the boiling point temperature. Thus, an azeotrope of A, B, C (and D . . . ) represents a unique type of relationship but with a variable composition which depends on temperature and/or pressure. Therefore, compositional ranges, rather than fixed compositions, are often used to define azeotropes. PA1 The composition can be defined as a particular weight percent relationship or mole percent relationship of A, B, C (and D . . . ), while recognizing that such specific values point out only one particular relationship and that in actuality, a series of such relationships, represented by A, B, C (and D . . . ) actually exist for a given azeotrope, varied by the influence of pressure. PA1 An azeotrope of A, B, C (and D . . . ) can be characterized by defining the compositions as an azeotrope characterized by a boiling point at a given pressure, thus giving identifying characteristics without unduly limiting the scope of the invention by a specific numerical composition, which is limited by and is only as accurate as the analytical equipment available.
At least one oxygen-containing additive gas such as O.sub.2, O.sub.3, CO, CO.sub.2, NO, and NO.sub.2 is optionally employed in concert with the nitrous oxide compositions of the present invention for plasma etching of thin film devices. Of the oxygen-containing additive gases, O.sub.2 is the most preferred.
At least one secondary additive gas is optionally employed in concert with the nitrous oxide compositions of the present invention for plasma etching of thin film devices. These secondary additive gases include fluorinated gases such as CF.sub.4, CH.sub.2 F.sub.2, CH.sub.3 F, CF.sub.3 --CF.sub.3, CF.sub.3 --CF.sub.2 H, CF.sub.3 --CH.sub.2 F, CF.sub.2 H--CF.sub.2 H, CF.sub.2 H--CFH.sub.2, CH.sub.3 --CF.sub.2 H, CH.sub.2 F--CH.sub.2 F, C.sub.3 F.sub.8, NF.sub.3, SF.sub.6, and well as ion-producing inert gases such as helium, neon, and argon.
A common reactor for carrying out the plasma etching utility of the nitrous oxide compositions of the present invention is a capacitively-coupled parallel-plate plasma processing reactor. Such reactors are widely used and well known in the semiconductor industry. A representative example of such a reactor system is described by Hargis, et. al., in a paper titled "The Gaseous Electronics Conference Radio-Frequency Reference Cell: A Defined Parallel-Plate Radio-Frequency System For Experimental and Theoretical Studies of Plasma-Processing Discharges" in the Review of Scientific Instruments, volume 65, 1994, page 140. Such a reactor is useful for precision etching of thin films of silicon; dielectric materials such as silicon dioxide, silicon nitride, silicon oxynitride, and doped dielectric oxides such as phosphosilicate glass, borophosphosilicate glass and other dielectric materials; conductive materials such as tungsten, molybdenum, titanium, tantalum and suicides of these materials as found on thin film devices, such as semiconductor wafers and flat panel displays; micro-mechanical devices; and similar structures employing semiconductor fabrication technology.
The plasma etching utility of the nitrous oxide compositions of the present invention is not restricted to the aforementioned reactor configuration, and can be employed in other systems useful for plasma activation of gaseous reactant species. Such systems include diode parallel-plate systems using either radio-frequency power (commonly at 13.56 MHz) or audio-frequency power (commonly in the range 100-400 Hz), or a combination of the previous two in systems commonly referred to as triode systems. In addition, the power can be alternatively applied by inductive rather than capacitive means, using a variety of planar and loop antennas known in the art; some such systems include helicon or helical resonator configurations, with other types of coupling also applicable. Additionally, microwave frequency excitation (commonly at 2.45 GHz) can also be used. A variety of configurations may be used, including but not limited to the configurations commonly referred to as electron cyclotron resonance (ECR) systems.